It's late June, here in New Zealand. We've had some very cold, wet and windy weather however, in the location where we saw the butterfly and several caterpillars, the day was bathed in sun and the area well sheltered.
The famous flight of the Monarch Butterflies, in North America each year, is well documented. Many thousands of them fly many thousands of kilometers to spend the winter in spectacular clusters on trees in California or in Mexico's cloud belt forests.
A study in New Zealand during the 1960s and 1970s tagged 6500 butterflies, of which 1011 were recovered. Only 28 butterflies flew more than 20 km and no pattern of migration was found.
In most parts of New Zealand, Monarch butterflies did not seem to go far afield and, as the weather gets colder, they head for local parks and gardens to cluster together.
During late autumn and early winter, you can sometimes see thousands of butterflies on one tree in public parks or wooded areas. Not a lot is known about the over-wintering behaviour of Monarch butterflies in New Zealand, but it does appear that they only form over-wintering clusters in areas where the temperature regularly falls below 10 0C.
On warm winter days the butterflies will fly from their clusters to feed on nectar. The butterfly we saw was certainly enjoying the nectar from lavender flowers on a gorgeous sunny Winter's day. The nearby swan plants had many fat Monarch caterpillars eating furiously in the sun - or were just basking. Lovely to see.
(Ref: Overwintering Monarchs NZ)